Method for producing refractory metals

ABSTRACT

A PROCESS FOR THE MANUFACTURE OF TITANIUM FROM TITANIUM TETRACHLORIDE BY REDUCTION WITH SODIUM, IN WHICH A PARTIALLY REDUCED MATERIAL PRINCIPALLY CORRESPONDING TO NA2TICL4 IS CONTINUOUSLY FORMED, IS IMPROVED BY CONTINUOUSLY MIXING THE PARTIALLY REDUCED MATERIAL WITH SODIUM AT A TEMPERATURE BELOW ABOUT 200*C. SO AS TO FORM AN INTERMEDIATE MATERIAL CORRESPONDING TO AT LEAST 15% BY WEIGHT NA3TICL4, COMPACTING THE INTERMEDIATE MATERIAL AT A TEMPERATURE OF LESS THAN 100*C. TO FORM A CONTINUOUS ROD OF THE COMPOSITE MATERIAL WITHOUT SUBSTANTIAL FURTHER REDUCTION OF THE TITANIUM CHLORIDE CONTENT THEREOF AND CONTINUOUSLY HEATING THE ROD FORMED AT TEMTERATURES ABOUT 800*C. TO COMPLETE REDUCTION OF TITANIUM CHLORIDE COMPONENT THEREOF, TO EFFECT SINTERING OF THE RESULTING TITANIUM METAL, AND TTO SIMULTANEOUSLY MELT THE SALT BY-PRODUCT AND THEREBY FACILITATE SEPARATION AND REMOVAL OF THE SALT FROM THE ROD-SHAPED, SINTERED TITANIUM METAL PRODUCT.

May 29, 1973 H, H, MQRSE ET AL 3,736,132

METHOD FOR PRODUCING REFRACTORY METALS Filed Dec. 17, 1971 PLL-00615??ET AL United States Patent O 3,736,132 METHOD FOR PRODUCING REFRACTORYMETALS Harold H. Morse, Cincinnati, and Cecil L. Easterday, deceased, byDorothy E. Easterday, representative, Washington Court House, and LayneS. Plock, Geneva, Ohio, and Fred K. Morgan, Cold Springs, Ky., assignorsto United States Steel Corporation, Pittsburgh, Pa.

Filed Dec. 17, 1971, Ser. No. 209,094 lnt. Cl. BZZE 1/00; C22b 53/00,61/02 U.S. Cl. 75-200 7 Claims ABSTRACT F THE DISCLOSURE A process forthe manufacture of titanium from titanium tetrachloride by reductionwith sodium, in which a partially reduced material principallycorresponding to NazTiCl.L is continuously formed, is improved bycontinuously mixing the partially reduced material with sodium at atemperature below about 200 C. so as to form an intermediate materialcorresponding to at least 15% by weight Na3TiCl4, compacting theintermediate material at a temperature of less than 100 C. to form acontinuous rod of the composite material without substantial furtherreduction of the titanium chloride content thereof and continuouslyheating the rod formed at temperatures above 800 C. to completereduction of the titanium chloride component thereof, to effectsintering of the resulting titanium metal, and to simultaneously meltthe salt by-product and thereby facilitate separation and removal of thesalt from the rod-shaped, sintered titanium metal product.

BACKGROUND OF THE INVENTION Quin, U.S. Pat. 2,827,371, describes aprocess for manufacturing titanium by reacting titanium tetrachloridewith metallic sodium at a temperature between about 200 C. and themelting point of sodium chloride in an agitated solid bed. There arenumerous problems encountered with this process. The reduction of thetitanium chloride with the sodium is a highly exothermic reaction and itis therefore necessary to rapidly remove the heat produced in order tomaintain the desired temperature. In many instances, hot spots in thereaction mixture are formed resulting in fused non-crystalline particlesof the metal in the final product. Additionally, since the reductionoccurs rapidly, there is little opportunity for crystal growth. Finally.it is necessary to sinter the final product in order to handle thetitanium in air.

An improved method of obtaining metallic titanium sponge and/or crystalsis described in Schott et al., U.S. Pat. 2.950.963. The titaniumchloride is continuously partially reduced with a controlled deficiencyof sodium and thereafter, in a batch operation, is brought into contactwith additional alkali metal, suicient for complete reduction, and thebatch heated for completion of the reduction and formation of the metal.This process is a hatch process and is not adapted to the manufacture oftitanium by a continuous process because the final reduction is soexothermic that the reaction mixture quickly loses processability. Themixture fuses and must thereafter be broken up to facilitate furtherhandling.

Accordingly, it is a principal object of this invention to provide amethod of manufacturing titanium continuously which eliminates thedificulties encountered in prior art methods, particularly the fusion ofthe reaction mixture. Other objects will become apparent to thoseskilled in the art from the following detailed description and drawing,in which the sole gure is a flow sheet of the process of the invention.

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SUMMARY OF THE INVENTION This invention relates to the manufacture oftitanium or zirconium. More particularly, the invention relates to animproved process for continuously producing titanium or zirconium inwhich a partially reduced material corresponding to a metaltetrahalide-sodium mixture in which about 45% to 55% of thestoichiometric reduction of the metal tetrahalide to the metal hasoccurred is continuously mixed with an alkali metal at a temperaturebetween 10D-200 C. to form an intermediate material corresponding to ametal tetrahalide-sodium mixture in which about 55% to 95% of thestoichiometric reduction to the metal has occurred, compacting theintermediate material at a temperature of less than C. to form acontinuous rod of the composite material without substantial furtherreduction of the metal halide content thereof, and continuously heatingthe rod thus formed at a temperature above 800 C. to complete reductionof the metal halide, to effect sintering of the metal and tosimultaneously melt the salt by-product and thereby facilitateseparation and removal of the salt from the sintered rod. The process ofthis invention provides a' continuous process in which the reactionmixture has good processahility at all stages of the process and inwhich the intermediate material can be compacted into the continuous rodwithout particles sloughing off or the application of undue pressures orthe use of temperatures which can cause alloying of the highly reactivemetal to any of the process equipment.

The invention also provides a non-compacted, nonaking intermediatematerial which can be compacted and extruded into a uniqueself-supporting, continuous rod without using undue pressure and withoutthe probability of sloughing off of particles from the reaction mass.

The unique self-supporting continuous rod, both sintered andnon-sintered is another feature of this invention. The continuous rodprovides a means of achieving a continuous reduction process and therebyconvert the semicontinuous, semi-batch process of the prior art into alarge scale, continuous commercial process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS While the invention isdescribed with particular reference to the manufacture of titanium fromtitanium halide, those skilled in the art will recognize that thedescribed process is similarly applicable to the production of zirconiumby the controlled partial reduction of zirconium halide.

ln the first step of the preferred embodiment of the invention, apartially reduced material, a TiCl4-Na mixture in which about 45% to 55%of the stoichiometric reduction to the metal has occurred, iscontinuously mixed with sodium. The partially reduced material isobtained in any suitable manner and preferably as described in the firststep of the aforementioned Schott et al patent.

In the Schott et al. procedure, titanium tetrachloride is reduced withan insuicient amount of sodium for stoichiometric reduction to themetal. Usually, hte sodium is employed at about 45% to 55%, preferablyabout 50%, of the theoretical amount required to completely convert thetitanium tetrachloride to titanium. The average composition of thepartially reduced material principally corresponds to NagTiCh, i.e., thecomposition, on the average, is equivalent to Na2TiCl4 (TiCl2:2NaCl).Such sodium titanium chloride complex, which can, of course, be admixedwith varying proportions of unreacted TiCl4 and varying proportions ofother partially reduced or totally reduced materials, will hereinafterbe referred ot as the reducer product because the reaction is usuallyaccomplished in a reactor commonly called the reducer,

The reducer product and sodium are mixed and partially reacted in aninert atsmosphere, such as argon, at a temperature between 100-200 C.,preferably about 130-160 C., to insure that complete reduction of thetitanium chloride content of the Na2TiCl4 to titanium does not occur. Attemperatures below about 100 C., either no reduction occurs or thereduction is so slow as to be impractical. At temperatures above about200 C., it is too dicult to practically control the degree of reaction.

The sodium employed in this step, hereinafter referred to as the mixingstep, is employed in an amount sucient to complete stoichiometricreduction of the reducer product to titanium metal and preferably aslight excess over the stoichiometric amount. Thus, the amount of sodiumemployed is generally about 50% of the theoretical stoichiometric amountnecessary to reduce the original amount of titanium tetrachloride totitanium and preferably, slightly in excess of 50%.

The mixing and further reducing is continued in the mixer until anintermediate product (mixer product) corresponding to a TiCl4-Na mixturein which about 55% to 95%, preferably about 75% of the stoichiometricreduction of the initial TiCl4 has occurred. At about 75% stoichiometricreduction, the reacted portion of the mass has u an average compositionprincipally corresponding to NasTiCl., and is in the presence of theremaining sodium for complete reduction. As the composition of the mixerproduct approaches 100% Na3TiCl4, the material approaches its lightestcolor and becomes extremely fluffy, with a high angle of repose, and hasthe appearance and consistency of dirty wet snow. Additionally, as theconcentration of the Na3TiCl4 complex approaches 100%, compaction, thenext step in the preferred process, can be performed at low pressuresand without particles of the mixer product sloughing off.

The reaction of the additional sodium over and above that required toform the Na3TiCl4 is very slow at the reaction remperature employed inthe mixing step. As a result, complete reduction to the metal is avoidedby cooling the mixer product to 100 C. or lower when the desired amountof complex has been formed without a significant amount of the complexbeing converted to titanium.

It is necessary to employ, as the mixer utilized herein, a. mixingdevice which does not put any appreciable force on the mix as would bedone in a paddle or dough mixer because the partially reduced materialwould pack and eventually jam the apparatus. Thus, any of the knownrotating tumbling type mixers can be employed. Mixers containing mixingblades or other mechanical parts which move relative to one another inwhich the reactants could be subjected to high unit pressures should beavoided.

While it is possible to form the mixer product in a single step withsome metal halides, such a procedure is generally impractical. Thetwo-step procedure of the present process allows the heat of reaction tobe controlled and does not result in the existence of hot spots in thereaction mixture.

In the next step of the preferred embodiment of the invention, the mixerproduct, cooled to less than 100 C., is compacted into a continuous rod.Incremental charges of the granular intermediate material arecontinuously compacted into a die and each charge is compacted againstand into engagement with a prior compacted charge to form the continuousbar or rod. The compacting is preferably accomplished under an inertatmosphere such as argon, and ambient temperature is generallyernployed. At this temperature, no substantial amount of furtherreduction of the titanium chloride content of the mixer product by thenon-reacted sodium in the material occurs.

By regulating the degree of reaction in the mixer product to produceprincipally Na3TiCl4, the compacting can be accomplished withoutemploying excessive pressure. lf

the average composition of the mixer product does not correspond to atleast 15 weight percent Na3TiCl4, it is necessary to use pressure inexcess of 4000 p.s.i. and even with such pressures, a substantial amountof the material will not compact into a continuous rod or will flake offthe rod formed.

1f the temperature is not below 100 C., further reduction will occurresulting in the production of titanium in a highly reactive state whilestill in the compactor which may alloy with the steel of the apparatus.As a result of precisely regulating the temperature and composition ofthe mixer product, no more than about 4000 p.s.i., and preferably about1000 to 3000 p.s.i. is needed to compact the granular mixer product intothe continuous rod.

Any appropriate compacting device known in the art could be employed inthis step such as, for example, the compacting devices described in}U.S. Pats. 2,651,952, 2,656,743 and 3,014,238.

The continuous rod thus produced is unique, and can only be producedwhen the foregoing procedures are employed. lt is self-supporting, andcan be fed wherever desired for subsequent processing. It is relativelyunreactive and stable under aimbient conditions.

The compacted rod or bar is thereafter heated to a temperature of atleast about 800 C. and preferably about 900-1500 C. The heatingaccomplishes three things: the remaining titanium chloride is reduced totitanium metal; the metallic sponge formed is sintered; andsimultaneously, the salt (NaCl) by-product is melted which facilitatesseparation and removal of the salt from the rod-shaped, sinteredtitanium metal product. Any temperature above the melting point of saltwill serve to complete the reaction and provide some sintering of thebar. Since salt can be removed during the heating, it is desirable toha-ve the temperature as high as is practical considering the equipmentand materials of construction in order to remove the maximum amount ofsalt and to secure the densest sintering.

The heating step is preferably accomplished under an inert atmospheresuch as argon and the rod is maintained at the sintering temperature forabout 1-10 minutes or more, preferably about 3-5 minutes. When vacuumconditions are employed, the salt left in the titanium can be reduced toless than 0.1% and subsequent purification can, if desired, be omitted.However, due to the problems involved in a vacuum operation at thesetemperatures, it may be preferable to operate under an inert atmosphere,and at or slightly above atmospheric pressure and to remove theremaining salt by a further purification procedure. In general, at leastand usually 85% of the total salt produced is separated during thisstep.

The sintered rod so produced is unique-it is very flexible when hot and,with proper guides, can be fed wherever desired for subsequentprocessing. The rodshaped, sintered titanium metal product generallycontains at least about 50% titanium, usually at least 60% and theremainder is salt.

The titanium thus produced is sufficiently inert so that when cooled, itcan easily be handled and does not react with air or water. Any saltremaining with the titanium can be further removed by any of the severalcontinuous processes known to those skilled in the art such as leaching,drip melting, plasma arc melting, and the like.

As an example of the preferred process of this invention, the figureshows the sequence of steps of the process. Sodium via line l, at a rateof 1210 parts per hour, and titanium tetrachloride via line 2, at therate of 5000 parts per hour, are continuously introduced into a stirredreducer 3 maintained under an argon blanket and controlled at atemperature of about -175 C. The resulting partially reduced material(reducer product), which is substantially all Na2TiCl4 is withdrawn vialine 4 from the reducer at a rate of 6210 parts per hour and introducedinto a mixer S. Additional sodium is introduced via line 6 into mixer 5at a rate of 1210 parts per hour. The particular mixer employed isdescribed in copending application Ser. No. 209,104, entitled Mixer ForPreparing An Easily Compactable Material, filed of e-ven date herewith,which is hereby incorporated by reference.

The temperature within mixer S is controlled at about 150 C. at thereaction zone thereof and decreased to about 90 C. at the outlet. Themixer product is continuously withdrawn from the apparatus via line 7 atthe rate of 7420 parts per hour. The mixer product thus formed containsabout 92% Na3TiCl4 and about 8% free sodium. The mixer product iscompacted at the rate of 7420 parts per hour at room temperature incompactor 8. The material enters a compacting section and is subjectedto a pressure of 2000 p.s.i. by means of a hydraulically operated ram.Continuous self-supporting rods of the compacted mixer product areprepared by the interlocking action of pressing one compact against thepreceding compact due to the irregular face of the piston head.

The resulting compacted rod is continuously withdrawn from compactor 8via conduit 9 and introduced into a tube 10 heated to 1100 C. by aninduction coil at the rate of 7420 parts per hour. Tube 10 can also beheated by resistance heat, or by a gas tired furnace, and the like. Therod is maintained in sintering tube 10 for about 3 minutes whenoperating at atmospheric pressure. The tube 10 has provision 11 fordrainage of liquid salt and 5210 parts per hour of sodium chloride,i.e., about 85% of the salt produced per hour, is removed. The sinteredrod is removed from the hot tube 10 via conduit 12 at a rate of 2210parts per hour. The thus formed sintered titanium metal rod containsabout 57% titanium and about 43% salt.

The rm, sintered titanium sponge is continuously fed vertically downwardinto a vertical tube furnace 13 and the lower end melted. The titaniummetal, free from salt impurity, is thereafter recovered at 14.

An atmosphere of argon is employed throughout the preparation of themetal.

It will be recognized by those skilled in the art that various changesand modifications can be made in the process and products of thisinvention without departing from the spirit and the scope thereof. Forexample, any of the multivalent metal halides and reducing agentsdisclosed in the aforementioned Schott et al. patent can also be used inthe process of this invention. The various ernbodiments of the inventionherein disclosed were intended to further illustrate the invention butnot to limit it. All temperatures have been stated in degrees centigradeand all parts and percentages by weight unless otherwise specied.

We claim:

1. In a process for the manufacture of titanium or zirconium fromtitanium tetrachloride or zirconium tetrahalide by reduction with analkali metal reducing agent in which a partially reduced materialcorresponding to a mixture of the metal tetrahalide and alkali metal inwhich about 45%55% of the total stoichiometric reduction of the metaltetrahalide to the metal has occurred is continuously formed, theimprovement which comprises:

(a) continuously mixing said partially reduced material with an alkalimetal at a temperature between 100-200 C. with regulating the feed rateof the respective reactants such that an intermediate materialcorresponding to a mixture of the metal tetrahalide and alkali metal inwhich about 55%-95% of the total stoichiometric reduction of the metaltetrahalide to the metal has occurred is formed;

(b) compacting the intermediate material thus formed at a temperaturebelow C. to form a eonunuous rod of the intermediate material withoutsubstantial further reduction of the metal halide content thereof; and

(c) continuously heating the rod at a temperature above 800 C. tocomplete reduction of the metal halide component thereof, to effectsintering of the resulting metal, and to simultaneously melt the saltby-product and thereby facilitate separation and removal of the saltfrom the rod-shaped, sintered metal product.

2. The process of claim 1 wherein the tetrahalide is tetrachloride andthe alkali metal is sodium.

3. In a process for the manufacture of titanium from titaniumtetrahalide by reduction with an alkali metal reducing agent in which apartially reduced material corresponding to a mixture of the metaltetrahalide and alkali metal in which about 45%-55% of the totalstoichiometric reduction of the metal tetrahalide to the metal hasoccurred is continuously formed, the improvement which comprises:

(a) continuously mixing said partially reduced material with an alkalimetal at a temperature between 100-200 C. while regulating the feed rateof the respective reactants such that an intermediate materialcorresponding to a mixture of the metal tetrahalide and alkali metal inwhich about 55%-95% of the total stoichiometric reduction of the metaltetrahalide to the metal has occurred is formed;

(b) compacting the intermediate material thus formed at a temperaturebelow 100 C. to form a continuous rod of the intermediate materialWithout substantial further reduction of the metal halide contentthereof; and

(c) continuously heating the rod at a temperature above 800 C. tocomplete reduction of the metal halide component thereof, to effectsintering of the resulting metal, and to simultaneously melt the saltby-product and thereby facilitate separation and removal of the saltfrom the rod-shaped, sintered metal product.

4. The process of claim 3 wherein the titanium tetrahalide is TiCl4 andthe alkali metal is sodium.

5. The process of claim 4 wherein the temperature in step (a) is about-160 C.

6. The process of claim S wherein the feed rates of the respectivereactants in step (a) are regulated such that an intermediate materialis formed corresponding to a titanium tetrachloride-sodium mixture inwhich about 75% of the total stoichiometric reduction of the titaniumtetrachloride to titanium metal has occurred and wherein theintermediate material is compacted in step (b) at a maximum pressure of4000 p.s.i.

7. The process of claim 6 wherein the rod in step (c) is heated to about900-1500 C.

References Cited UNITED STATES PATENTS 2,824,799 2/ 1958 Hansley et al.75-223 2,880,084 3/1959 Schott et al. 75--84.5 2,950,963 8/ 1960 Schottet al. 75-84.5

CARL D. QUARFORTH, Primary Examiner B. HUNT, Assistant Examiner v.UNITEDSTATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3 f 736 :132Dated May 29 1973 g Harold H. Morse et al. lnyentods) a It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the heading'ztovthe printed specification, lines 7 and 8, "assignorsto lUnited States Steel Corporation, Pittsburgh, Pa." should read-eassignors by direct and mesne assignments l/.Z interest toNationalDistillers and Chemical Corporation, New YArk, N. YI.-', a corporationof Va., and l/Z interest to United Statesl Steel Corporation,Pittsburgh, Pa. a corporation of Del.

Signedand sealed this 27th day of August 1974.

(SEAL) Attest: MCCOY M. GIBSON, JR. C.MARSHALL DANN Attesting Officier`Commissioner of Patents FORM Po'wso (1o-G9) UscoMM-oc ooa1e'pe9 n UAS.GOVERNMENT PRINTING OFYICE I 0 366-33.

vUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,736,132 Dated May 29, 1973 i Harold H. Morse et al. Inventods) It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as show-n below:

In the heading tothe printed specification, lines 7 and 8, "assignors toUnited States Steel Corporation, Pittsburgh, Pa." should read assignorsby direct and mesne assignments l/Z interest toational Distillers andChemical Corporation, New YArk, N.-

a corporation of Va., and l/Z interest to United States SteelCorporation, Pittsburgh, Pa. a corporation of Del.

Signedand sealedA this 27th day of August 1974.

(SEAL) Attest: y

MCCOY M. GIBSON, JR. omARsHALL DANN Attesting Officer Commissioner ofPatents

